Stabilization of propylene polymers

ABSTRACT

Polymers of propylene of increased stability against oxidative deterioration containing a compound of the general formula:   WHEREIN X IS AN INTEGER FROM 1 TO 2, AND EACH R individually is an alkyl radical of 1-4 carbon atoms.

United States Patent 11 1 Robin et a].

[451 May 6,1975

[ STABILIZATION OF PROPYLENE POLYMERS [75] inventors: Michael Robin,Colonia, N.J.;

Sheldon R. Schulte, Columbus, Ohio [73] Assignee: Ashland Oil, Inc.,Ashland, Ky.

[22] Filed: May 8, 1972 [21] App1.No.: 251,165

3,057,926 10/1962 Coffleld et a1. 260/4595 3,070,569 12/1962 Rosenthal260/4595 3,129,213 4/1964 Worrel 260/4595 C 3,377,333 4/1918 Ciesielskiet a1, 260/609 F 3,406,158 10/1968 Brown et a1 260/4595 C 3,647,8853/1972 Geering et a1. 260/4595 C OTHER PUBLICATIONS ACS Meeting Div.Organic Coatings and Plastics Chemistry 21, No.2, 1961, pp. 79 to 106.

Primary Examiner-Dona1d E. Czaja Assistan! Examiner-Eugene C. Rzucidlo[57] ABSTRACT Polymers of propylene of increased stability againstoxidative deterioration containing a compound of the general formula:

wherein x is an integer from 1 to 2, and each R individually is an alkylradical of 1-4 carbon atoms.

15 Claims, No Drawings STABILIZATION OF PROPYLENE POLYMERS BACKGROUND OFTHE INVENTION The present invention relates to the stabilization ofpropylene polymers against oxidative deterioration. More particularly,the present invention is concerned with polymers of propylene ofincreased stability against oxidative degradation which contain certaintris phenol sulfides.

Propylene polymers may be formed into many useful articles. However,such polymers are susceptible, in varying degrees, to degradation causedby exposure to light. Severe degradation occurs when the polymer isexposed to light in the ultraviolet portion of the spectrum. Inaddition, the unstabilized polymer is degraded by oxygen, especiallywhen subjected to elevated temperature and/or mechanical working.Degradation apparently results from free radical formation, whichformation is promoted by mechanical work, heat, ultraviolet light, andimpurities such as metals and metal compounds.

The free radicals which are formed undergo further chemical reactions,resulting in undesirable chemical and physical transformations in thepolymer. Thus, after a variable period of time, there is a prematuredeterioration of the polymer. Such deterioration may result in a loss intensile strength, molecular weight and other desirable properties suchas pliability and impact strength. In addition, discoloration andembrittlement of the polymer may be observed.

Numerous materials have been suggested as antioxi dant additives forsuch polymers but various of these materials are not altogethersatisfying either in terms of their versatility and/or performance understringent conditions of temperature and mechanical working, andparticularly at temperatures of 250 F and higher. Accordingly, thesearch for improved methods of protecting propylene polymers proceedsquite actively.

Those skilled in the art have long recognized the empirical nature ofantioxidant technology and the extreme difficulty of predicting whethera propylene polymer will be effectively stabilized against oxidation bythe incorporation of a given compound. Whether any commerciallyworthwhile level of oxidation protection is attained and the extentthereof depends both upon the nature of the material to be protected andthe exact structure of the antioxidant compound, and is most frequentlyunpredictable. Thus, Downey and Zerbe, in US. Pat. No. 2,670,382,observed that it is now known that the number, size, position and kindof substituted group [in the antioxidant compound] exerts a profoundinfluence on the antioxidant properties of the substituted phenolsulfides." A typical comment on the influence of the material which isto be stabilized may be found in Modern Plastics, Volume 37, page 192,Jan. 1960, which states: Of all the problems that polypropyleneproducers have faced, stabilization has been perhaps the most difficult.Polypropylene, when it is unstabilized, deteriorates rapidly uponexposure to heat or ultraviolet light. The difficulty with proper stabilization of polypropylene is that in general, the vast numbers ofstabilizers for other polyolefins, vinyl chlorides and the like provedineffective for polypropylene. It was necessary to develop uniquesystems for specific end uses." Moreover, the empiric nature of the artof stabilizing polyolefins with phenolic stabilizers was rec- OH OH 11%csnll 5 11 S ll 5 ll and metal salts of such compounds, were discussedby Cook and W. Thomas. They disclosed in U.S. Pat. No. 2,336,074 thatsuch compounds would stabilize lubricating oils against oxidation andsludge formation. Later, Downey et al, in US. Pat. No. 2,670,382.suggested that oxidation inhibitors for rubbery polymers could beproduced by reacting two molecular equivalents ofa 3,6-di-substitutedphenol with one molecular equivalent of sulfur dichloride to produce ahis phenol sulfide such as one having the following structure:

C H C211 HO OH C 31 C3iI7 Downey et al reported that attempts toincrease the sulfur content of the phenol sulfide produced compositereaction products including some compounds which contained more than twophenol nuclei linked together by sulfur atoms. Downey et al seem toindicate that the presence of compounds containing more than two phenolnuclei caused some loss in the antioxidant properties of the compositereaction products as compared with the his phenol sulfide in the rubberypolymers.

Apparently in conformity with the negative teachings of Downey et al,the rather comprehensive disclosure of Salyer and Kenyon in US. Pat. No.2,985,6l7 relative to phenol sulfide thermal processing co-stabilizersfor Ziegler polyethylene and polypropylene fails to discuss a singletris phenol sulfide. Also, although Bailey's US. Pat. No. 3,067,259relative to alkoxy substituted phenolic stabilizers for polyethylene andpolypropylene includes a general formula for trinuclear phenolsembracing a myriad of methylene, ethylidene, isopropylidene and sulfurbridges tris phenols, not one specific tris phenol sulfide compound isdiscussed.

More recently, in US. Pat. No. 3,423,389, Wheelus has reported that hisand higher phenol sulfides are helpful in improving the color and colorretention of tall oils and rosin compounds during bleaching. Due to thedifferences which exist between these compounds and the lubricating oilsand polymers discussed by the BRIEF SUMMARY OF THE lNVENTlON The presentinvention is directed to a propylene polymer composition of increasesstability against oxidative degradation containing propylene and aneffective stabilizing amount of compound of the general formula:

O H OH OH Q 4 X x@ 4% R R R wherein .r is an integer from l-2 and each Rindividu ally is an alkyl radical of 1-4 carbon atoms.

The present invention is further concerned with increasing the stabilityof the propylene polymer against degradation caused by thermalprocessing which comprises incorporating in said polymer prior tocompletion of the thermal processing an effective stabilizing amount ofcompound of the general formula:

wherein and R have the same meanings as defined above.

DESCRIPTION OF PREFERRED EMBODlMENTS The propylene polymers to which thepresent invention is applicable are solid homopolymers of propylene andsolid copolymers of propylene and one or more cthylenically unsaturatedcopolymerizable monomers. Generally the propylene polymers contain atleast about 85 percent by weight of propylene units. Some examples ofsuitable ethylenically unsaturated comonomers which are copolymerizablewith propylene such as for instance styrene. vinyl chloride. inylacetate. vinylidene chloride. vinylidene chlorofluoride.methylmethacrylate. butadiene. isoprenc, ethylene. butylene.lethylbutene-l. 4-methyl-pentene-l. 4.4'dimethylpcntene4.3-methylpentene-l. and the like. Thus. any propylene polymer within theforegoing definition or mixtures of such polymers may be em ployed.whether it includes a molecular structure which is crystalline. oramorphous or both.

Any of the available methods may be used to prepare the propylenepolymers. Non-limiting examples of appropriate production methods forpropylene polymers are those involving the polymerization of propylenein the presence of catalysts disclosed in Belgian Pat. Nos. 530(1l7.533362. 535082 and 538782.

Propylene polymers prepared by the processes described above havemelting points of from l00 C to 300 a tensile strength of from l.000 to10.000 lbs. per square inch and a molecular weight of from 6.000 to3.000.000 and preferably 20.000 to 1.000.000. Usually a mixture ofcrystalline and amorphous polymer is obtained. if desired. the amorphouspolymer can be separated from the crystalline polymer by contacting amixture thereof with a hydrocarbon solvent. such as isooctane orn-heptane at an elevated temperature. The amorphous polymer issubstantially soluble under these conditions. whereas the Crystallinepolymer is substantially insoluble.

In accordance with the present invention. a polymer of propylene asdescribed above has incorporated therein a tris phenol sulfide of thegeneral formula:

wherein is an integer of from 1 to 2. and each R individually is analkyl radical of l-4 carbon atoms. in the above formula is preferablyequal to l.

The tris phenol sulfides in accordance with the above formula areemployed in a small but effective amount. The amount is sufficient toprovide at least some protection to the polymer against the effects ofthermal processing. Such small but protective amount is usually withinthe range of about 0.005 to about 5 weight percent. based upon theweight of the polymer and preferably from about 0.01 to about 1.5 weightpercent based upon the weight of the polymer.

The tris phenol sulfides encompassed within the above formula areconveniently obtained by the action of sulfur monochloride (SQClg) orsulfur dichloride (SCl on a 4-alltylphenol and a Z-butyl Lalkylphenol ina suitable solvent medium. When convenient or desirable. other methodsof synthesis may be used. and it is to be understood that this inventionis not limited to any particular method of synthesis but pertainsbroadly to the use of the materials described. Also. while the compoundsto be used in accordance with the present invention have been describedwith the aid of a structural formula. it will be appreciated that someif not all of the available production methods may produce minorquantities of other molecules derived from the starting materials whichdo not correspond exactly with the structural formula. Usually thequantity of such impurities is less than about 10 percent and most oftenless than about 5 percent by weight of the desired tris phenol sulfide.These other materials may or may not be separated from the depicted trisphenol sulfide before their use in the invention. and it shouldtherefore be understood that the claims appended hereto are intended tocover the use ofthe essentially pure tris phenol sulfide compound aswell as composite reaction products in which they are the majorcomponent(s). The weight of those other compounds in the compositereaction products which are effective in stabilizing the polyolefms maybe counted with the weight of the tris phenol sulfide compound of theabove formula in determining the amount of said compound which ispresentv The present invention is of particular importance in increasingthe stability of the propylene polymer against degradation caused bythermal processing whereby the sulfide is incorporated in the polymerprior to completion of the thermal processing and preferably isincorporated while the polymer is still at about room temperature. Thesulfides employed according to the present invention are preferablyutilized for pro tecting propylene polymers during thermal processing attemperatures of about 250 F to about 450 F and preferably attemperatures of about 300 to about 350 F.

There are numerous methods that can be used to treat propylene polymerswith tris phenol sulfides in accordance with the invention. One methodis to incorporate the tris phenol sulfide during cold milling of thepolymer. i.e.. during the treatment of the polymer on conventionalrubber mills without the addition of exter nal heat. ln order to obtainmaximum dispersion of the tris phenol sulfide in the polymer. it ispreferred that the phenol sulfide be dissolved in suitable solvent.e.g.. methanol. ethanol. benzene. toluene. and that the resultingsolution be added to the polymer on the rolls. Ordinarily. a volatilesolvent is used which will readily evaporate. although if the intendeduse of the polymer permits or renders desirable the incorporation ofahigh molecular weight diluent for the purpose ofplasticizing orotherwise affecting the polymer. this may be done. The tris phenolsulfide can also be incorporated in the polymer in other mixing devices.for example. Ban burry mixers and extruders. The polymer can be dissolved in a solvent. for example. hot aromatic hydrocarbons such asbcnzene or xylene. followed by mixing the tris phenol sulfide in properproportions with the polymer solution and the use of said solution forcasting films. spinning fibers and similar operations that are wellknown to the art. wherein the solvent is evaporated away from thepolymer. resulting in the formation of films. fibers. mono-filaments andthe like. Moreover. finely divided particles of the polymer may beslurried in a solvent solution of the tris phenol sulfide compound.following which the solvent is evaporated to leave the particles ofpolymer intimately admixed with the tris phenol sulfide compound.

It will be understood that in any of these methods of treating thepolymer with the phenol sulfide. during such treating. or before orafter. conventional fillers. dyes. pigments. modifying polymers. and thelike can be admixed with the ethylene polymers described above.

The following non-limiting examples are provided to further illustratethe present inventionv All parts are by weight unless the contrary isstated.

EXAMPLE 1 To a glass reaction vessel equipped with an agitator. athermometer. a condenser to which is connected a means for scrubbingevolved HCl are added with agitation 750 parts toluene. 216 partsparacresol. and e56 parts of Z-t-butyl-4-methylphen0l. While maintainingthe temperature between 20 and 30 C. 424 parts of sulfur dichloride areadded with agitation over a period of approximately 2-3 hours. duringwhich HCl is evolved. Upon completion of the addition. the reactionmixture is agitated at room temperature for an additional hour. Thereaction mixture is then heated to 40 C and is held at that temperaturefor l to 2 hours to insure completion of the reaction as evidenced bycessation of HCl evolution. 750 parts of water are added to the reactionmixture with vigorous agitation. The agitation is stopped and themixture is transferred to a separating funnel. The mixture stratifiesinto a lower aqueous layer and upper organic layer. The lower aqueouslayer is removed and discarded. To the remaining organic layer are addedwith agitation 500 parts of water and 50 parts of a 10 percent aqueousdisodium hydro' gen phosphate solution. The agitation is continued untilthe organic layer. water. and phosphate are thoroughly mixed. Theagitation is then stopped and the mixture upon standing stratifies intoa lower aqueous layer and an upper organic layer. which is nowessentially neutral. The aqueous layer is removed and discarded. Theremaining organic layer is washed twice with 500 parts of water and theresidual water and solvent are removed by vacuum distillation. 985 partsof a.o'-thio( 3- t-butyl-2-hydroxyS-methylphenyll-p-cresol are obtained.

EXAMPLE 2 The above procedure is repeated except that one mole of sulfurmonochloride is substituted for each mole ofsulfur dichloride. l l00parts of a.a'-dithio( 3-1- butyl-lhydroxy-S-methylphenyll-p-cresol areobtained.

EXAMPLE 3 To a glass reaction vessel equipped with an agitator. athermometer. a condenser to which is connected a means for scrubbingevolved HCI are added with agitation l525 parts toluene. 270 partsparacresol. and l030 parts 2.4 di-t butylphenol. While maintaining thetemperature between and C, 515 parts ofsulfur dichloride are added withagitation over a period of approximately 23 hours. during which HCl isevolved. Upon completion of the addition. the reaction mixture isagitated at room temperature for an additional hour. The reactionmixture is then heated to C and is held at that temperature for l to 2hours to insure comple tion of the reaction as evidenced by cessation ofHCl evolution. L500 parts of water are added to the reaction mixturewith vigorous agitation. The agitation is stopped and the mixture istransferred to a separating funnel. The mixture stratifies into a loweraqueous layer and upper organic layer. The lower aqueous layer isremoved and discarded. To the remaining organic layer are added withagitation 500 parts of water and parts of a 10% aqueous disodiumhydrogen phosphate solution. The agitation is continued until theorganic layer. water. and phosphate are thoroughly mixed. The agitationis then stopped and the mixture upon standing stratities into a loweraqueous layer and an upper organic layer. which is now essentiallyneutral. The aqueous layer is removed and discarded. To the remaininglayer are added with agitation 500 parts of water and 50 parts of a It]percent aqueous disodium hydrogen phosphate solution. The agitation iscontinued until the organic layer. water. and phosphate are thoroughlymixed. The agitation is then stopped and the mixture upon standingstratifies into a lower aqueous layer and an upper organic layer. whichis now es sentially neutral. The aqueous layer is removed and discarded.The remaining organic layer is washed twice with 500 parts of water andthe residual water and sol vent are removed by vacuum distillation. 1000parts of a.a'-thio( 3,5-di-t-butyl-Zhydroxyphenyl l-p-cresol areobtained.

EXAMPLE 4 To a glass reaction vessel equipped with an agitator. athermometer. a condenser to which is connected a means for scrubbingevolved HCl are added with agitation L175 parts toluene. 225 parts of4-t-butylphenol. and 620 parts of 2.4-di-t-butylphenol. While maintaining the temperature between and C. 318 parts of sulfur dichloride areadded with agitation over a period of approximately 2-3 hours. duringwhich HCl is evolved. Upon completion of the addition. the reactionmixture is agitated at room temperature for an additional hour. Thereaction mixture is then heated to C and is held at that temperature forl to 2 hours to insure completion of the reaction as evidenced bycessation of HCl evolution. L500 parts of water are added to thereaction mixture with vigorous agitation. The agitation is stopped andthe mixture is transferred to a separating funnel. The mixturestratifies into a lower aqueous layer and upper organic layer. The loweraqueous layer is removed and discarded. To the remaining organic layerare added with agitation 500 parts of water and parts of a 10 percentaqueous di sodium hydrogen phosphate solution. The agitation iscontinued until the organic layer. water. and phosphate are thoroughlymixed. The agitation is then stopped and the mixture upon standingstratifies into a lower aqueous layer and an upper organic layer. whichis now essentially neutral. The aqueous layer is removed and discardedvThe remaining organic layer is washed twice with 500 parts of water andthe residual water and solvent are removed by vacuum distillation. 929parts of a.a'-thio( 3.5-di-t-butyl-Z-hydroxyphenyl )-4-tbutylphenol areobtained.

EXAMPLE 5 The product prepared according to Example I is admixed with apolypropylene of 0.90 density and approximately 325.000 molecular weightand is available under the trade designation Pro-Fax 650l from Hercu lesin a steel container and the mixture is extruded twice at 380 F. Theresulting polypropylene composi tion containing 0.5 percent by weight ofthe product prepared according to Example 1 is then pressed into a 6-6.5mil film at 350 F and 1280 psi on a 10 inch hydraulic ram press.Likewise. there are prepared according to the above procedure a film ofthe same polypropylene without any antioxidant and films of the samepolypropylene containing 0.5 percent of the following:

a,a'-thio(B-t-buty'lQhydroXy-S-methylphenyl)-pmcthoxyphenol;2.6-his(3t-butyblhydroxy-S-methylhenzylr4- methylphenol;2.2'-thiobis(fi-t butyl-4-methylphenol);2.2'-methylenebis(6-t-butyl-4-methylphenol);2.6-bis(2hydroxy-3methoxyfi-methylbenzyl)-4- methylphenol;a.a'-thio(3.5di-t hutyl-lhydroxyphenyl)-4-tbutylphenola.a'-thio(3.S-dimethyLZ-hydroxyphenyl)-p-cresol;

a .a '-thio( 3-nonyl2-hydroxy-5-methylphenyl )-pnonylpheno] EXAMPLE 6The polypropylene films produced in Example 5 are simultaneouslyintroduced into a forced draft oven which is continuously maintained at1': 1 C. The absorbence of the films in the carbonyl region. 5.8 micronsof the IR spectrum is then recorded periodically. When absorbencereaches 94 percent the sample is considered to be oxidized," and thetime of exposure to reach this point is recorded in the table below;

'Jirnt: in Mrs. to Reach 94% gidit i g Amount Absorbence H OH OH (R) 11(2 s -@s c 11 0.5% 3.80

CH CH CH (1, 3-thio(3tbutyl-2-hydroxy5 methylphenyl)-p-cresol (Productprepared according to Example 1] Home 8 OH OH OK (c) 11 0 O s s c n 0.5%91 CH OCH CH 0. ,ct -t.hio 3-t-butyl-2-hydroxy-5- methylphenyl) p--methoxyphenol Continued gtaitive Amount Time in Hrs.

to Reach 94% Absorbence H II OH (D) H9C4 O CH 0 Cii j C 13 0.5% 118 C11C11 C 0;; OH v. (E) ligc S 4:19 (L570 15 CH3 CH3 2 2 -thiobis6--t--butyl-4methylphenol) 011 Oil c /J\ (F) ll jc LojT- z'/T ln O 69 ICH CH 2 2 nethylenebis 6tbutyl4 methylphenol) n on 011 (G) 11 C O s O 5'6 C II 0 5% 157 -thio(3 5-di-t-butyl-2- hyd roxy'phcnyl)-4-t--butylphenol H 01 OH (H) H C s 5 5 (6; CH 0.5% 89 CH3 CH C11 0. ,u.'th5 o 3 5-dimethyl-2-hydroxyphenyl) -cxesol (Product prepared accordingto Example 4) H H H (1) ti e s s 0 0 x 0.5% 15 H3 C13 CH3 (1,(If-this)(3-nonyl-2-hydroxy- S-met'nylphcnyU-p-cresol (Product preparedaccording to Example 3) demonstrates the unexpected excellentstabilization with trisphenol sulfides which do not contain an alkoxy 6ssubstituent as required in the Bailey patent. In addition.

a comparison of Example 6(A) with Example 6(D) demonstrates the presenceof sulfur bridges between the phenolic nuclei provides for much moreeffective stabilization as compared to similar materials wherein thesulfur bridges are replaced with methylene bridges. In addition. acomparison of Examples ME) and (at demonstrates that the substitutionofa sulfur bridge between phenolic nuclei for a methylene bridge doesnot necessarily provide improved stabilization. A comparison of ExampleMA) with ()(El shows that the presence of three phenolic nuclei providesgreatly iniproved stabilization as compared to the presence of only twophenolic nuclei in the compound. Moreover. comparison of Examples bl A land MG with Examples NH} and htll further demonstrates the improvedresults obtained from materials of this invention as compared tomaterials not containing butyl groups ortho to the hydroxy radicals ofthe two end phenolic radicals The following examples if provided tofurther demonstrate the unpredictability in selecting antioxidants. Thisexample shows that some of the above antioxi- Ill l2 tions. Theresulting polyethylene composition is then pressed into a 641.5 mil filmat 3 lll F and 1.180 psi on a ll) inch hydraulic ram press. Likewise.there are pre pared according to the above procedure a film of the samepolyethylene without any antioxidant and films of the same polyethylenecontaining (1.1 percent of the following:

o.o'-thio( 3-t-butyl-lhydroxy-5-methylphenyl l-pmethoxyphenol; andrt.a'-thiot -t-buty l-Z-hydroxy-5methylphenyl l-pcresol.

The resulting films are then subjected to 125 1 C in a forced draftoven. The absorbance in the carbonyl region of the IR Spectrum L98microns) is then recorded after periods ofexposurc. When absorhancereaches 94 percent the sample is considered to be oxidized." and thetime of exposure to reach this point is recorded in the table below Timein Hrs.

to Reach 9414 H OH OH c S O 5 C 5 0.1% 864 (2 11 c n c n 0:,Ctthio( 35-ditbutyl2 hydroxyphenyl)pcresol (Product prepared according to Example3) l None 59 OH OH Oi (C) H C s r O s 153 c 11 0. 1% 1661 CH CH CH (La'-thio(3tbutyl2hydroxy-5 methylp'nc-nyl) -p-cresol (Product preparedaccording to Example 1) on on on tn) 1620 OCH CH dants within the scopeof the present invention do not provide the same type of results whenincorporated in a similar material such as polyethylene as are obtainedwith the propylene polymers. Some of the materials within the scope ofthis invention; however. provide good stabilization when incorporated inpolyethylene.

EXAMPLE 7 The above example points out that a material which is aneffective antioxidant with one polymer is not necessarily effective whenemployed with another polymer For instance. a comparison of Example 7(Aland Example 7(C) shows that a.a'-thio(3,5-di-t-butyl-lhydroxyphcnyl)-4-t-butyl which demonstrates goo results when added topolypropylene. is considerably worse than a material outside the scopeof this inven tion which contains a methoxy group. On the other hand. acomparison of Examples 7(() and 7(1)) indicates that materials withinthe scope of this invention are also effectne in polyethylene. Certainmaterials other than a.a"thio( 3-tbutyl-Z-hydroxy-S- methylphcnyllp-cresol within the scope ofthis invention such ttistlytr-llllttl3.5wild-hut)l-3-l1}LlTU\)]7llClt)'ll p-c resol; how ever. arealso effective in polymers of ethvlenc.

EXAMPLE 8 The product prepared according to Example I is admi\ed with apolypropylene of 0.90 density and 315.000 molecular weight a ailableunder the trade wherein is an integer of from l to R is tertiary butyland each R individually is an alkyl radical of l4 carbon atoms.

2. The composition of claim 1 wherein said propydesignation Pro-Fin6.50! from Hercules in a steel 5 lens pllll'mer WlYP PY W container andthe mixture is extruded twice at 380 F The ctlmpnsllllm f cllllm 1 l VThe resulting polypropylene composition containing ThelctlmpusllllmL'llllm \"hcrcm R 05 percent by weight of the product prepared accord-15 l' 0T l t 5 l l bg l l ls zi i z f sl Ka Ill 5. The composition olclaim 1 wherein said com- H L pound is ata thiot3tbut\'l-ZhydroW-S-press likewise. there are prepared according to the p ymeth\lphen\l)-p-cresol.

ahtn'e-described method. a film ot the same polypro- A v pylene withoutany antioxidant and films of the same COmPOSIUUn l Claim t m saidcompolypropylene containing 0.5 percent of a.a"thio(3.5- H pound is an-thio(3.5-di-t-hutyl-lhydroxypheny]ldi-t-hutyl-Z-hydroxyphenyl)-p-cresol.

The pol\prop\lene films produced above are introi i 7. Th om ositim ofclaim I whwein said comduced into a lorced dratt oven which iscontinuously Ound z r t 51 but 'l h j u. maintained at l50 I C Theabsorbence of the films p p i t-hutylphenol. m the carbonyl region. 5.8microns ot the IR spectrum. an is then recorded periodically, Whenahsorhence 8. The composition of claim I which contains from reaches 94percent the sample is considered to be oxiabout 0.005 to about 5 weightpercent of said comdized." and the time of exposure to reach this pointis pound based upon the weight of said propylene poly recorded in thetable below: mer.

Tili'ii in Mrs.

to l-l'x'fcll will, fi lit ivr Amount mnnoxpt-ncc- H O31 O11 t (A)l-lgC4 O 51 O S C H 0.5% 152 l c11 cn c12 (Product prepared according toExample 1) (B) None 4 1-! OH H (C) H C S S C 13 0.5% 170 C4H9 CH3 C4 19thio(3 5-di-t-butzyl-2- hydroxyphenyl)-pcresol (Product preparedaccording to Example 4) Thu ahmc cwmplc further mustmmg tho imprmycd 9.The composition of claim I which contains from aout0.0l )1 it ,1stabilization obtained trom the materials employed in b d l l f e h lthe present invention, For instance Examples MA) upon 1 k pmmlcncpulland MC} demonstrate the unexpected increased stahii Th0 compmmunufcmm 1 wherein id pulvmcr lization with trisphenol SLtllltlCS which donot contain cumpmcs M him About 85 percent by weight ut-pr'upv anttlls'UX} suhstituent as required in the Bailey patent. 1

What is claimed is. v ll. The composition ol claim 10 wherein said coml.A polymer composition of increased stability pound i t l-n 43 b Llh l jagainst osidatne degradation comprising a propylene ih l h l)- polymerha ing an elfecti e stabilizing amount of com- 12 Thg composition f l i10 wherein pound oi the general formula: 6U pound isa.a'thio-(3,5-di-t-hutyl-2 hydroxyphenyl)-pcresol.

13. The composition of claim 10 wherein said conillll l UH pound isa.a'-thio(3 5-di-t-butylQ hydroxyphenyl)-4- V g L; W tbutylphenol. i l Km 14. The composition of claim 10 wherein X is l.

15. The composition otclaim [0 wherein each R in dividually is methyl ortert. butyl.

1. A POLYMER COMPOSITION OF INCREASED STABILITY AGAINST OXIDATIVEDEGRADATION COMPRISING A PROPYLENE POLYMER HAVING AN EFFECTIVESTABILIZING AMOUNT OF COMPOUND OF THE GENERAL FORMULA:
 2. Thecomposition of claim 1 wherein said propylene polymer is polypropylene.3. The composition of claim 1 wherein x is
 1. 4. The composition ofclaim 1 wherein each R individually is methyl or tert-butyl.
 5. Thecomposition of claim 1 wherein said compound is Alpha , Alpha''-thio(3-t-butyl-2-hydroxy-5-methylphenyl)-p-cresol.
 6. The compositionof claim 1 wherein said compound is Alpha,-thio(3,5-di-t-butyl-2-hydroxyphenyl)-p-cresol.
 7. The composition ofclaim 1 wherein said compound is Alpha , Alpha''-thio(3,5-di-t-butyl-2-hydroxyphenyl)-4-t-butylphenol.
 8. Thecomposition of claim 1 which contains from about 0.005 to about 5 weightpercent of said compound based upon the weight of said propylenepolymer.
 9. The composition of claim 1 which contains from about 0.01 toabout 1.0 weight percent of said compound based upon the weight of saidpropylene polymer.
 10. The composition of claim 1 wherein said polymercomprises at least about 85 percent by weight of propylene.
 11. Thecomposition of claim 10 wherein said compound is Alpha , Alpha''-thio-(3-t-butyl-2-hydroxy-5-methylphenyl)-p-cresol.
 12. Thecomposition of claim 10 wherein said compound is Alpha , Alpha''-thio-(3,5-di-t-butyl-2-hydroxyphenyl)-p-cresol.
 13. The compositionof claim 10 wherein said compound is Alpha , Alpha''-thio-(3,5-di-t-butyl-2-hydroxyphenyl)-4-t-butylphenol.
 14. Thecomposition of claim 10 wherein X is
 1. 15. The composition of claim 10wherein each R individually is methyl or tert. butyl.